Some microelectronic devices have bump bond structures with copper pillars and tin-containing solder on the copper pillars. The solder is reflowed (melted) during a bump bond process which attaches the bump bond structures to leads of a package structure such as a lead frame. When the molten tin-containing solder wets the copper, copper-tin intermetallic compounds form around the interface of the copper pillars and the tin-containing solder. Voids may also form in the copper pillars close to the intermetallic compounds. The intermetallic compounds and the voids adversely influence the solder joint reliability, by degrading the mechanical and electrical properties of the joints.